Reinforced bridge superelastic bone compression staple and inserter system

FIELD OF THE INVENTION

The present invention relates to a room temperature superelastic bone compression staple and staple inserter system intended for bone fixation in the surgical management of fractures and reconstruction of the foot and hand, and more specifically, the staple is a two-legged staple with an improved bridge and shoulder configuration to distribute loading in insertion and use.

BACKGROUND OF THE INVENTION

Initial bone staples were temperature activated memory staples, which were rendered obsolete through the adoption of mechanically activated room temperature superelastic Nitinol devices as the relevant materials technology advanced to the current state of the art.

Over 1.8 million orthopaedic trauma fixation procedures were performed in the US in 2016, which is expected to remain the fastest growing segment through to 2025 and is expected to reach over $4 billion by 2025, and the fastest growing part of this market is the staple fixation segment. The primary driver for growth is reportedly a reduced operating time as compared to screws, and plates.

While this growth demonstrates that orthopedic arts have accepted bone staples as an alternative and even a preferred fixation hardware to screws and bone plates for certain procedures, there remain issues and limitations to the designs presently available. While the latest generation of memory staples have improved rigidity and compressive capability when used alone or as adjunctive hardware, (which could improve outcomes for certain procedures, such as the Lapidus arthrodesis), it is still desirable to provide a stiffer and stronger construct and more reproducible surgical technique than the generally accepted perpendicular arrangement of legs and bridge used for example for a first metatarsophalangeal arthrodesis procedure. Additionally, the prior art devices are not optimal for fracture and osteotomy fixation of the hand and foot, including joint arthrodesis and to stabilize and dynamically compress bone fragments to facilitate osteosynthesis.

In response to these and other concerns, the present staple has a low-profile design to respect the economy of space in small bone procedures and further is designed for quick and efficient use, including removal following bone fusion. As used herein, “low-profile” means that the staple includes a bridge member having a bottom surface that is so close as possible, and may contact the bone. In addition, the staple has shoulders between the legs and bridge that flares to distribute force unto the underlying bone at this point.

Additional issues with the prior art staples include problems with packaging, implant or instrument breakage (including shearing of the legs or fracture at the bridge member), incompatibility with the staple inserter or other related instruments, lack of compression or sustained compression within the bone/implant construct, and difficulties with the instrument and implantation process.

A known risk with the prior art staples is associated with over-spreading the staple, which can over-stress the staple legs and have a deleterious effect on mechanical properties, recoverable strain and fatigue resistance. As the art has dealt with this problem, other risks associated with bridge strength have arisen. The present invention reduces this risk through design improvements achieved in design of the leg/bridge interface, i.e. at the “shoulders” of the staple, as well as for the bridge member itself through the addition of a thickened area or “node, flanked on either side by narrowed areas or “fillets” or waists”. In the present invention, a sinuous configuration provides that the shoulders flare in width and thickness out of the legs and into the bridge to form a “hood” at the shoulder which wraps the bone. The bridge narrows into a first and second waist, which have a width and thickness similar to the legs, and which then flare outward again to the thickened area which forms opposing nodes that together form the two apexes of a “diamond” (although the points may be rounded to avoid stress points).

The present staple has a unique configuration that addresses the issues of breakage while providing a low profile implant that is particularly well suited for small bone procedures. The staple and staple inserter are designed to first hold the staple in position for insertion and then to function together to avoid over-spreading and/or misalignment of the staple legs so as to reduce potential use risks and to provide a device which is inherently less prone to user error. In addition, the staple is designed for permanent implantation or unlike prior art devices, for removal following bone fusion which can typically take 4-6 weeks while the patient is partially weight bearing. Specific instrumentation is provided for the removal procedure.

The staple will be manufactured from ASTM F2063 room temperature superelastic (e.g., from 2 to up to 8%) Nitinol. (and it will be understood that other shape memory materials can be used in this design).

SUMMARY OF THE INVENTION

The present invention relates to a superelastic Nitinol staple having a pair of spaced legs joined by a bridge member is “straight-backed” meaning that it extends along an axis to form a “table-top” type of configuration more notable in the energized state in which the legs are substantially transverse to the bridge member, however, with a rounded top surface. In fact, the top surface can be advantageously curved in one or two dimensions, i.e., along the axis and transverse to it to provide a segment of a sphere or torroid, especially when the legs are in the converging position. This provides a staple having a low profile straight-backed configuration which suits implantation in the small bone environment, in particular for use in osteotomies, fusions or other osteo synthesis procedures.

The staple is fabricated by machining a blank to form a staple in the closed (converging legs) shape and the resulting staple is mechanically deformed during use to induce the superelastic shape memory properties to compress bone segments and facilitate osteosynthesis. Alternatively, the staple can be formed as a flat straight bi-laterally symmetrical (about both the medial and the longitudinal axes) blank with an intermediate area including three thickened areas, one to form either shoulder at the bridge leg bend, and one in the middle of the bridge. After forming, the legs are bent on either side to form the U-shaped configuration.

The staple has a bridge member preferably having an optimal configuration with a thickness defined between an exterior and corresponding opposing interior surface and a width defined between two side edges, and where one of the thickness and the width have a thickened or reinforced area provided by a flare or swelling of material such as to form an edge member with a profile that is a serpentine or a half diamond shape with fillets on either side of a v or bump. The opposing edge members flare at the same point along the length of the bridge to form symmetrical profiles. The result is the formation of a partial diamond flanked by two narrower straits that widen again into the shoulder area. This reinforcement serves to inhibit the potential for failure at the bridge.

The legs may be joined to the bridge member by corner extensions or “shoulders” which flow into the legs or may extend directly from the bridge for example from an inwardly curved recess in the ends of the bridge member. The legs preferably have a uniform cross-sectional shape which helps to eliminate stress risers, for example, at the conjunction of the legs and bridge. The bridge and shoulders are “tuned” to optimize stress. Once past the shoulder region, the legs generally are uniform cross-section due to ease of mfg. The invention could further include legs that widen at the bottom to form a paddle for osteoporotic applications. The staple is designed for optional removal, so that while the staple may include texturing, ridges, or barbs to improve the hold in bone, the amount of mechanical interference is limited, for example by the provision of low ridges and on one only one or two surfaces of the legs, such as on the inner surface facing inward on the leg. Thus, the staple design permits easy removal.

The staple is provided having a range of different bridge lengths and various leg lengths in the same range of length, so as to accommodate different fixation procedures in the forefoot, midfoot, rearfoot and hand. The staple is typically provided in sizes in which the dimensions of the bridge are 10 to 25 mm in length; 1 to 6 mm and preferably 1.5 to 5 mm in width; with a maximum width at the node of 2.5 to 6 mm, and preferably 3 to 4 mm; and with a minimum width on either side of the node of 1.5 to 3 mm and preferably 2.2 to 2.6 mm, and having leg lengths of 5 to 20 mm, and preferably of 7.5 to 15 mm, with staple being provided at integrals of 3 mm bridge and leg lengths.

In addition, the staple is part of a system with includes a staple inserter, and where the bridge reinforcement helps to hold the staple on the inserter. The staple can be supplied pre-assembled on an inserter or introducer in a sterile procedure pack containing disposable instrumentation.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. <b>1</b></figref> shows a top perspective view of the staple with the legs in a converging state and in accordance with the present invention;

<figref idref="DRAWINGS">FIG. <b>2</b></figref> shows a top view of the staple of <figref idref="DRAWINGS">FIG. <b>5</b></figref>;

<figref idref="DRAWINGS">FIG. <b>3</b></figref> shows a first side view of the staple of <figref idref="DRAWINGS">FIG. <b>2</b></figref> with a cross section of the narrow section of the bridge as shown in <figref idref="DRAWINGS">FIG. <b>2</b></figref>;

<figref idref="DRAWINGS">FIG. <b>4</b></figref> shows a second side view of the staple of <figref idref="DRAWINGS">FIG. <b>2</b></figref> with a cross section of the thickened section of the bridge as shown in <figref idref="DRAWINGS">FIG. <b>2</b></figref>;

<figref idref="DRAWINGS">FIG. <b>5</b></figref> shows a side view of the staple of <figref idref="DRAWINGS">FIG. <b>1</b></figref>;

<figref idref="DRAWINGS">FIG. <b>6</b></figref> shows a bottom side perspective of the staple of <figref idref="DRAWINGS">FIG. <b>1</b></figref>;

<figref idref="DRAWINGS">FIG. <b>7</b></figref> shows a bottom detail view of the staple of <figref idref="DRAWINGS">FIG. <b>1</b></figref>;

<figref idref="DRAWINGS">FIG. <b>8</b></figref> shows a side view of the staple of <figref idref="DRAWINGS">FIG. <b>1</b></figref>;

<figref idref="DRAWINGS">FIG. <b>9</b></figref> shows a bottom perspective view of a staple in the activated state with the legs in parallel position and having shoulder optimization in accordance with the present invention;

<figref idref="DRAWINGS">FIG. <b>10</b></figref> shows a bottom perspective view of a staple in the activated state with the legs in parallel position and having bridge and shoulder optimization in accordance with the present invention;

<figref idref="DRAWINGS">FIG. <b>11</b></figref> shows side perspective of a drill guide body for the implantation of a four-legged staple in accordance with the present invention;

<figref idref="DRAWINGS">FIG. <b>12</b></figref> shows a side perspective view of a staple inserter loaded with a four-legged staple for use in the drill guide body and with the inserter system of the present invention;

<figref idref="DRAWINGS">FIG. <b>13</b></figref> shows a side perspective view of an inserter staple cartridge member loaded with a two-legged staple in an activated state ready for use with the inserter system of the present invention;

<figref idref="DRAWINGS">FIG. <b>14</b></figref> shows a full side view of the activator member for use with the inserter system of the present invention loaded with a two-legged staple in accordance with the present invention;

<figref idref="DRAWINGS">FIG. <b>15</b></figref> shows a side perspective detailed view of a further embodiment of the inserted staple cartridge member loaded with a two-legged staple and of the inserted system of the present invention;

<figref idref="DRAWINGS">FIG. <b>16</b></figref> shows a side perspective view of an inserter staple cartridge member of <figref idref="DRAWINGS">FIG. <b>15</b></figref> loaded with a two-legged staple with the rails of the inserter truncated in order to show the groove members on the inside of the rails to guide the diamond bridge of the staple;

<figref idref="DRAWINGS">FIG. <b>17</b></figref> shows an alternative inserter staple cartridge member with truncated legs and loaded with a four-legged staple for use with the inserter system of the present invention;

<figref idref="DRAWINGS">FIG. <b>18</b></figref> shows a bottom side perspective of a four-legged staple in accordance with the present invention;

<figref idref="DRAWINGS">FIG. <b>19</b></figref> shows a side view of the staple of <figref idref="DRAWINGS">FIG. <b>18</b></figref>;

<figref idref="DRAWINGS">FIG. <b>20</b></figref> shows a bottom view of the staple of <figref idref="DRAWINGS">FIG. <b>18</b></figref>; and

<figref idref="DRAWINGS">FIG. <b>21</b></figref> shows a top view of the staple of <figref idref="DRAWINGS">FIG. <b>18</b></figref>.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a room temperature superelastic Nitinol bone compression staple <b>10</b>. The staple <b>10</b> has two or more legs <b>12</b> that will engage bones or bone segments through the cortical surfaces. The legs <b>12</b> are spaced apart from each other and joined together by bridge member <b>14</b> that extends across the area between legs at either end of the bridge member <b>14</b>. As shown, the legs are joined to transitional areas <b>16</b> or shoulders which flare outward in width compared to the width of the leg and of the bridge to which they join and fold or curve at an angle of from 75° to 90°, and preferably from 85° to 90° relative to a long axis of the bridge member <b>14</b> to form a hood shape as can be seen in <figref idref="DRAWINGS">FIGS. <b>6</b>-<b>8</b></figref>.

The bridge member <b>14</b> has a top surface <b>20</b> and a bottom surface <b>22</b> which have corresponding shapes so that they are separated by a constant thickness for at least a portion, and preferably for at least 50%, and more preferably for at least 75% or even 90% of the surface area and further has a complex curving configuration. It extends along an axis preferably in a straight profile, but with a topography that can curve in either of two dimensions (i.e. length and width) or in both of two transverse directions. The shape includes two side edges <b>24</b>, which have the complex curving shape (which looks somewhat like a curly bracket “{”) of the present invention.

The bridge member <b>14</b> includes a thickened or reinforced area <b>40</b> provided by a flare or swelling of material such as to form an edge member with a profile that is a serpentine or a half diamond shape with fillets or concave curves <b>42</b> on either side of a node, v-shape or bump <b>44</b>. The opposing edge members flare at the same point along the length of the bridge to form symmetrical profiles. The result is the formation of a partial diamond <b>46</b> flanked by two narrower straits <b>48</b> that widen again into the shoulder area. This reinforcement serves to inhibit the potential for failure at the bridge.

The surfaces extending between the side edges <b>24</b> forming the top or outer surface <b>20</b> and the bottom or inner surface of the bridge <b>22</b> curve along the axis, in a shape that may define a portion of a circle, and they curve as well in a direction transverse to the axis. Preferably the bridge curves along the length. It is also possible that the bridge curves along the width. In this instance, both curves are convex relative to the bottom surface and can be the same or different radius curves. Preferably, the curves have the same inner radius dimensions so that the bridge member defines portions of spheres on the outer and inner surfaces and the radius is between 10-100 mm, and optimally is 50 mm +/−10 mm.

The legs <b>12</b> also have a regular shape. While this can be a rectangle, they can form other polygons in cross section. The legs may also include features <b>30</b> to help hold the legs in the bone, such as texturing, or ridges or barbs that help to hold the legs in position. Preferably, the surfaces of the legs that include this feature are opposing surfaces, such as surfaces that face an opposing leg as shown in the detail of <figref idref="DRAWINGS">FIG. <b>6</b></figref>. These ridges may include a series of spaced parallel ridges or alternating areas which in cross-section extend away from the base surface of the leg and return the base surface of the leg. Alternatively, the legs may include a series of grooves cut into the surface, or the legs may have a surface treatment, such as knurling, or cross-hatching. If they have ridges, the ridges may cover a portion of the vertical surface, such as 10-90%, and preferably from 25-50%. The ridges are lower profile than barbs, (for example only 0.25-2, and preferably 1+/−0.25 mm in height from the surface of the leg in order to permit earlier staple re-orientation and increased bone growth after removal.

a pair of opposing legs, either one or two legs may include these features. The legs have a cross-sectional configuration that provides for improved resistance to breaking as well as increased compressive forces, such as a polygonal shape that is not square. One preferred configuration is a rectangle. The staple may have two opposing legs, spaced apart from each other along the axis of the bridge member, or on one side it may have two legs, and one on the other, or optionally, it may have four legs which are situated to form a rectangle which circumscribes the bridge member. The staple is provided having a range of different bridge widths ranging from 10 mm to 25 mm and various leg lengths in the same range of length, so as to accommodate different fixation procedures in the forefoot, midfoot, rearfoot and hand.

<figref idref="DRAWINGS">FIGS. <b>18</b>-<b>21</b></figref> illustrate a four-legged version <b>111</b> of the staple of the present invention. This staple has a bridge <b>122</b> which joins four legs <b>112</b> which may include the ridges <b>120</b> of the two-legged version of the staple. This version of the staple includes the hooded shoulder members or flares <b>116</b> which join each of the legs to the bridge which has a central inward curve to accommodate the sliding relationship with the inserter rails that have opposing convex curves to capture the inward curves of the bridge member. Thus, the bridge has a central waist area <b>123</b> that functions to interact with the inverse curved surfaces of the inserter rails to guide the staple along that length. <figref idref="DRAWINGS">FIG. <b>20</b></figref> shows the complex topography which forms the reinforcing attributes of the shoulder members.

<figref idref="DRAWINGS">FIGS. <b>9</b> and <b>10</b></figref> illustrate finite element analysis that demonstrates the advantages of the staple <b>10</b>, <b>10</b>′ of the present invention. <figref idref="DRAWINGS">FIG. <b>9</b></figref> only having the flared optimized shoulders <b>16</b>′ as a transition between the bridge <b>14</b>′ and the legs <b>12</b>′, while <figref idref="DRAWINGS">FIG. <b>10</b></figref> also includes the diamond area <b>44</b>.

The staple system of the present invention also comprises a companion four-legged staple <b>111</b>, shown on a further embodiment of the inserter cartridge <b>80</b> in <figref idref="DRAWINGS">FIG. <b>12</b></figref> as well as in <figref idref="DRAWINGS">FIGS. <b>17</b> and <b>18</b></figref> that illustrate the hooded shoulder feature and curving bridge member of the present invention on a multi-legged staple member. The inserter cartridge <b>80</b> fits on an inserter body and activator member <b>70</b> with handle <b>60</b> and used with a drill guide assembly <b>150</b> having a variation of the turn member <b>174</b>′. This version is also shown with an additional component <b>228</b> that inserts into a bore in the drill guide and has arms that secure and stabilize the inserter during the implantation of the staple into the pre-drilled bores. The four-legged staple includes legs <b>112</b> and a bridge member <b>114</b> that may also include the bridge optimization of the present invention.

<figref idref="DRAWINGS">FIGS. <b>13</b> and <b>16</b></figref> illustrate how the nodes <b>44</b> or diamond member <b>40</b> of the bridge <b>14</b> of the staple <b>10</b> of the present invention are constrained and guided along the length of the inserter in mating surfaces such as in a recess, i.e., a slot <b>332</b> or a groove '<b>332</b> formed on the side legs <b>320</b> of a staple cartridge <b>310</b> on an embodiment of the staple inserter <b>300</b> where internal surfaces <b>334</b> interface with the area between the fillets <b>42</b> and the nodes <b>44</b> of the bridge member to secure the staple <b>10</b> in the staple inserter cartridge <b>310</b> and while the staple legs <b>12</b> are held by the end of the staple cartridge <b>310</b>. In the four-legged version the staple bridge may include the concave surfaces while the cartridge legs include convexly rounded surfaces that hold the waist. <figref idref="DRAWINGS">FIG. <b>16</b></figref> illustrates a further embodiment of the staple inserter and staple cartridge assembly <b>300</b>′ in which the cartridge has a close-pin type capture mechanism for the staple <b>10</b>, and a collar <b>350</b> that holds the cartridge <b>310</b>′ to the inserter <b>300</b>′.

<figref idref="DRAWINGS">FIGS. <b>17</b>-<b>21</b></figref> illustrate a four-legged version of the invention having the enhanced bridge and shoulder configuration.

<figref idref="DRAWINGS">FIGS. <b>12</b>-<b>14</b></figref> illustrate a drill guide body <b>200</b> having a handle <b>210</b> and extensions <b>212</b> that include grooves <b>214</b> that receive drill guide members for a four-legged staple <b>226</b> or for a two-legged staple <b>228</b> as shown in <figref idref="DRAWINGS">FIGS. <b>13</b> and <b>14</b></figref>.

Preferably, the staple is fabricated by machining a Nitinol blank to form a staple in the closed (converging legs) shape and the resulting staple is mechanically deformed during use to “load” the staple, meaning to induce the superelastic shape memory properties to compress bone segments and facilitate osteosynthesis. In this state, the staple has legs extending at a substantially transverse direction to the axis of the bridge in order to allow the staple to be inserted into pre-drilled pilot holes in the bone.

Optimally, the staple is supplied pre-assembled and pre-loaded into a parallel leg configuration on an inserter <b>110</b> or introducer in a sterile procedure pack containing disposable instrumentation. In this instance, the inserter <b>110</b> has a pair of pivoting handles <b>120</b> that are squeezed together to expand a pair of arm member bearing cylindrical holders that bias the staple legs open when the handles are engaged together.